Low TA - unclear whether action is needed or not.

[lalittle]

I have an in-ground plaster pool, app 25,000 gal. Using a Taylor K-2006 test kit (as well as another less expensive kit, just for comparison) I've watched my Total Alkalinity drop over the last several weeks. It used to be a little over 100 -- perhaps even as high as 120 -- but now it's down around 70 to 80. I assume this is probably because I have to add muriatic acid once a week or so in order to keep the pH down. I'm not sure why the pH creeps up, but I'm told that it could be due to the "relatively" new plaster (about a year or so old), as well as the fact that my water supply has a higher pH (at the top of the color test scale on a Taylor K-2006.) The consistent addition of the acid, however, would seem to explain the lowering TA.

What I'm not clear about is whether or not action needs to be taken. I've read over this forum, along with various other pool info web sites, and I see totally contradictory advice on this. Some people say that it's crucial to raise the TA to 100 using baking soda, and that not doing this could cause damage to the pool surfaces and equipment. Others, however, say that keeping TA in this lower range is actually advised in order to combat the rising pH condition. I have noticed that as the TA has dropped, the rising pH has slowed, which would seem to concur with the later response. If this is detrimental to equipment, however, I would obviously want to raise the TA. I also read that higher CYA levels can inflate the TA test, and given that my CYA is 70 to 90 or so, this would imply that my TA is even lower. Others say that CYA in the low 100's is just find, and does not need to be factored in to the TA results.

The net result is that I'm totally unsure what to believe, so I'm looking for any feedback I can get on this.

My general levels are as follows:

FC 3 (using Trichlor tablets and liquid chlorine to raise/shock as needed.)
CC 0
pH 7.5 (rises to 7.8, then I lower it to 7.4 using liquid muriatic acid)
CH 375 (my water source is fairly hard)
TA 70 to 80
CYA 70 to 90

Thanks for any feedback on this,

Larry

 

[257WbyMag]

Most people's pools have a pH rise just naturally. If you have a SWCG, you will have to contend with rising pH for as long azs you operate the cell. New plaster always rises to a degree; some, moreso than others. You can control the rate of pH rise in these situations to a certain degree by making adjustments, usually downward, in your TA. A lower TA will decrease the frequency of which you have to add acid.

Most pool stores and printed resources say that for a swimming pool, a TA in the 100 to maybe 120 range is ideal. Many of us have found though that our pools tend to do better with a lower TA, say, around 70 to 80. I tend to add acid about once a weekto bring my pH down to between 7.2 to 7.8. As a result of my acid additions, my TA has settled out at around 70. I have found that if I kinda ignore my TA and just add acid when my pH indicates that I need to, my TA will find its "happy place" for lack of a better term. Over the years, it has remained at 70 to 80 fairly constantly and this is without my messing with it.

If I were you, I would just add acid when you need to lower your pH and just see where your TA ends up.

Are you running a SWCG? If not, I would consider lowering your CYA. If your CYA is truly 70 and you are not running a SWCG, your water doesn't have enough FC to sanitize.

 

[zea3]

Your TA is just fine. Minimum for TA is 70, and if it drops below 70 it is easy to raise with baking soda. Since your CH is a little high you want to keep the TA around 70 and the pH between 7.2-7.5 to prevent scale formation. We rarely recommend using adjusted alkalinity for the TA result.

Your real issue is your CYA. Unless you use a saltwater chlorine generator, 70-90 is too high for CYA. According to The Pool Calculator, with a CYA of 70 ppm your recommended FC range is 5-10. Since your latest test shows FC 3 ppm, you are below the minimum recommended level and are at risk of developing algae. You should stop using trichlor tablets (and any other dry chlorine), use liquid chlorine for daily FC levels, and drain and replace 1/3 of your water to lower the CYA level to around 50 ppm. Trichlor and dichlor dry chlorines will continue to raise the CYA level until it becomes problematic for your pool. Calcium hypochlorite will raise the CH level, which is already high in your pool. Liquid chlorine will not add any CH or CYA to the pool.

 

[lalittle]

Without the trichlor tablets, my chlorine seems to drop pretty fast -- I end up having to add liquid chlorine a lot more often (I use liquid to avoid issues with CH, as you noted.) This in turn raises the pH even faster, which means even more acid all the time. By using the tablets, things seem to be a lot more "stable," so it would be nice if I could continue to use the tablets.

If I drain enough of the pool to get the CYA down to 50 or so, would I then be able to use the trichlor tablets without worrying about the CYA jumping up too quickly? How long will it take for the CYA to rise again? I find that using about 3 tablets a week results in a pretty stable chlorine level, with only occasional additional chlorine needed. I did see the table that indicates a higher chlorine level is needed with my higher CYA, but so far, even with FC levels in the 2 to 3 range, sanitation has not been an issue for me. I've yet to experience any issues like algae, and the water looks very clear and clean.

I do not use a SWG, but I keep reading that a TA of 100 is what I should shoot for. This is what Taylor -- as well as numerous other sites -- tells me to try for, and that 80 (rather than 70) is the minimum. This is why it's so confusing -- the opinions on the "proper" level for TA seem to vary quite a bit, with some saying that 70 is fine, while others saying that if it's 70, you should absolutely raise it. Is the consensus here that a TA of 70 is "fine," or is it actually "ideal" in order to prevent scale buildup? In other words, what would the "perfect" TA value be in my situation?

Thanks again for the feedback,

Larry

PS. I actually have another question about CYA, but I'll put that in a separate thread to avoid confusion.

 

[dmanb2b]

Proper TA levels depend on your chlorine source. If you want to use Trichlor, than TA in the 100-120 range is OK as Trichlor is acidic and that why your PH rise seems to stablize. Think of a trichlor tab as a mix of chlorine, CYA and acid :lol: The net effect of adding bleach is that it is PH neutral, so with TA at 100, PH will tend to rise, especially in a newer plaster pool. If you want to use bleach TA at 70 is recommended.

There are folks here than run SWGs and have spas (aeration causes PH rise too) that need to keep TA in the 50-60 range to slow PH rise.

You should post your CYA question here as well

 

[anonapersona]

3 tablets a week, if 7 oz tablets, is 21 oz of trichlor which gives 25K gallon pool an extra 3.2 ppm CYA a week. Per the Pool Calculator. So, in 6 weeks you get 19.2 ppm CYA build-up.

If you drain 50% now, to ~40 ppm, then go another 6 weeks as you have been, you will be back at 60 ppm which a bit beyond the an upper limit. If that is the end of the swim season, maybe OK, close the pool and let rain and snow dilute it until next year.

You may want to test the fill water TA, I suspect it is near or above the 120 ppm that the pool was at earlier. So the refill will push up TA (and pH upward drift) and then you will see that ease over time via the trichlor tabs and continued muriatic acid additions.

You can do this, you just have to pay attention to the numbers. I assume that fill water will not introduce metals or other new problems.

If you do not adjust TA upwards by some method, as it gets lower, below maybe 60, it gets unstable and can crash suddenly. Bad things can happen to metal parts in equipment and you don't want that.

 

[lalittle]

The thing that confuses me about the FC/CYA charts is that even though they were created by very knowledgeable people and seem perfectly logical, they contradict what might be called the "official" information out there, including that from reputable companies like Taylor, as well as official organizations like the Association of Pool and Spa professionals and the National Swimming Pool Foundation. For example, when using CYA at 50 (that maximum "target" level according to most literature), the chart says to use a target FC level of 6. According to the "National Swimming Pool Foundation" chart in the Taylor literature, however, the maximum target level of FC is only 4, and the overall max level is only 5. In other words, the absolute highest recommended FC level recommended by this organization is still BELOW the target level recommended by the FC/CYA chart.

On top of this, the highest "safe" level of FC recommended by the EPA is only 4.

This leads to an important question: When using the higher FC levels (in order to compensate for the higher CYA), is the effect on skin/health and swimsuits the same as it would be with lower CYA and lower FC? For example, if I use CYA 30 and FC 4, according to the chart this has the same sanitation effect as using CYA 90 and FC 10. Is the effect on skin and swimsuits ALSO the same in both situations?

I've always been concerned with Chlorine levels, so I've always tried to keep it down to 3 or so in order to be "safe" on skin and fabric. Do I understand correctly that as CYA goes up, using higher FC levels will have the same effect on skin or fabric as lower CYA and lower FC levels did? In other words, are these "other" effects caused by chlorine ALSO are reduced by the higher CYA?

Thanks again,

Larry

 

[pepsiholic]

I don't know anything about the scientific aspect of it, I can just tell you what I know from personal experience. I keep my cya at around 50, with maintaining my chlorine levels around 5-6, and I have never had a problem with bathing suits fading or dry skin. I have been using this method for 2 years and my black bathing suit is still very black.

 

[dmanb2b]

We get this question often...and there is plenty written by chemgeek in the deep end to help understand, but in simple terms, CYA binds with chlorine and the more CYA is in your water the more FC is bound to it. So yes a pool with CYA at 50 with FC at 6ppm has a MUCH lower active chlorine level than a pool with 1ppm FC and no CYA.

Here is a link referenced in the FC/CYA chart that has multiple references quoted.

chlorine-cya-chart-t2346.html

 

[lalittle]

Thanks again for all the information. (Of course, now I'm spending WAY too much time reading about this.)

I noticed on this page http://www.poolsolutions.com/gd/best-guess-swimming-pool-chlorine-chart.html that it appears that if I use CYA at 30 to 50, I could shock a pool to 15ppm and still swim in it immediately with absolutely no issues (since this still falls into the light green colored square.) Am I reading this correctly? I always thought that FC at shock levels was damaging to fabric and could be unhealthy. I've always been told (prior to this point) that when you shock a pool, you need to let the level drop to "normal" levels before swimming in it. Is swimming in shock levels, as this chart indicates, really not an issue?

Thanks,

Larry

 

[lalittle]

On a side note: If I haven't seen any sanitation issues using my current FC levels (which are too low according to the CYA/FC charts), does this mean that I shouldn't mess with the levels, or have I simply been lucky up to this point? I can't help feeling a bit of "don't mess with it if it isn't broken," but I also want to make sure that I prevent problems from ever starting in the first place.

The thing that really strikes me in all this is that "most" people I talk to with with non-SWG pools use trichlor tablets as their primary FC source and don't worry about too much CYA. I hear this all the time -- i.e. "just use the trichlor tablets and add a little liquid chlorine when needed." Based on the information here, however, their CYA levels should be through the roof after a relatively short period of time. Based on the pool calc, my CYA should be going up 16ppm a month (minus splash out, which I really don't have much of.) My experience over the past couple months, however, doesn't really agree with this -- i.e. my CYA has just not risen by all that much. With 4 ppm CYA a week added to my pool (according to the chart), my CYA should be MUCH higher.

Why the discrepancy between the information here and the numbers that I'm seeing in my pool?

Thanks,

Larry

 

[dmanb2b]

Long term I prefer swimming in water that has an a FC of 7.5 - 12.5% of CYA. But yes we do consider anything lower than shock level safe to swim in.

I think about it this way...think of all the thousands of pools out there, where folks listen to pool store advice and shock weekly. 1st they are likely not shocking (shocking is a process, not a product), but how many of those folks have no clue how much water their pool holds and just dump in a few bags of powdered chlorine for good measure

For the most part they live to tell the story. The key hamrful chlorine aspect in pools is CC, which is the chlorine you smell. In a properly maintained pool, CC is at 0.5ppm or below.

I'm sure if Richard (chemgeek) reads this, he can shed some light on the science behind it.

 

[dmanb2b]

The CYA test in the K2006 or the TF100 can only measure FC to within +/-15ppm. A lot of pool owners have no idea what their CYA level is and high CYA is not a big problem, until you have a problem. That same set of folks stick with the "shock weekly" program too...so in reality the low FC is not consistently low.

Anyhow you are getting the picture...TFP is now 25K+ members strong. Pool Forum(Poolsolutions) and BBB was around way before TFP too. All I can tell you is that following these methods, I never shock my pool and most everyone swears I do not have a chlorine pool, rather a "salt" pool since they can't smell the chlorine.

Tabs can work well too, but understanding how they impact your water chemistry is crucial and that is what BBB is all about, consistent testing with a good kit and maintaining a proper FC/CYA relationship...perform and overnight FC loss test every now an then and make sure CC is 0.5ppm or less and you are BBB'g

 

[zea3]

If you dig a little deeper, you may find that they also drain the pool every few years. Pool stores are fond of telling customers they have "old" or "stale" water that needs to be replaced. In addition if you have a lot of rain, draining the overflow also lowers CYA.

 

[chem geek]

I've written about the higher FC levels with CYA in the water in this post and you can see where state regulations for Free Chlorine (FC) exceed the EPA drinking water limit for several states in this post. However the real proof of the FC/CYA relationship comes from multiple scientific peer-reviewed papers as well as ORP field measurements as described in the "Chlorine/CYA Relationship" section in this post, not to mention the tens of thousands of real pools on this and other forums.

The Chlorine / CYA Chart has a minimum FC that is roughly 7.5% of the CYA level for non-SWG pools. This is roughly equivalent in active chlorine (hypochlorous acid) concentration to a pool with only 0.06 ppm FC and no CYA. Even the shock level which is roughly an FC that is 40% of the CYA level has an active chlorine concentration equivalent to a pool with only 0.6 ppm FC and no CYA. The minimum level comes from that amount required for chlorine to kill algae faster than it can grow in almost all pool conditions (i.e. regardless of phosphate and nitrate level) and was initially determined by Ben Powell of The PoolForum and PoolSolutions. With CYA in the water, most of the chlorine is bound to it and while not inert, it is much, much less reactive -- scientific sources show oxidation power 1/100th that of hypochlorous acid and disinfection power may be even lower than that. Fortunately, most pathogens are relatively easy to kill so these low active chlorine levels that are enough to prevent algae growth are also reasonable to kill pathogens quickly as shown in the chart in this post (the protozoan oocyst Cryptosporidium parvum being the notable exception, but where even chlorine with no CYA doesn't inactivate it quickly).

As for why so many "official" sources in the pool/spa industry are so wrong when it comes to chlorine/CYA, TA levels and the true source of rising pH, the net pH effect of chlorine sources, the 10x rule for breakpoint chlorination, the need to shock a pool regularly, the best way to lower TA, etc. it is more inertia than anything else. Someone decades ago makes an incorrect analysis (usually a non-scientist), gets everyone else in agreement, and everyone just repeats this information without actually looking at the chemistry nor at what happens in real pools. That's not how we operate here at TFP. We look at multiple sources of peer-reviewed scientific papers and validate as much as we can in real pools and spas as well as with various experiments. We only care about truth, not what some so-called industry expert proclaims. Also, there are very strong financial incentives in the multi-billion dollar pool chemical industry that discourage the full disclosure of materially important information that you would need to know to make an informed purchase decision.

As for why your CYA has not apparently risen that much, wait more than just a month or two due to errors in the CYA test (as noted in the previous posts). In my own pool years ago I used Trichlor pucks/tabs in a floating feeder and had a low 0.7 ppm FC per day chlorine usage since the pool wasn't used during the week and I have a mostly opaque pool cover. I have an oversized cartridge filter that only needs cleaning once a year so no dilution from regular backwashing and I originally pumped winter rain water into the sewer and not into the pool (and we don't get summer rains). So I have very little water dilution and my CYA went from 30 ppm to 150 ppm after around 11 months of pool use over 1-1/2 seasons (during the winter, chlorine usage becomes almost nil). 30+0.7*30*11*0.61 = 171 ppm which with some splash-out and some oxidation of CYA from chlorine makes 150 ppm a quite rational and reasonable number. That's when I started to get nascent algae with the pool turning dull and chlorine usage going up, in spite of my using algaecide but only every other week.

Also note that high CYA with a low FC does not guarantee algae growth. One could have low algae nutrient levels in the pool or have algaecide and not even know it (such as copper ions found in some Trichlor pucks/tabs). CYA may not climb as fast because of weekly backwashing of sand filters, summer rain overflow, short swim seasons and smaller pool sizes, and CYA loss over the winter.